Database

Chapter 22. Database

Caution when using the database

Caution

At the time of writing, the software described in this chapter is still in
an experimental stage, and loss of data is possible. Please ensure that you
have an alternative backup copy of your data before committing to database
usage.

Preparation

To access the database, KMyMoney uses the SQL module supplied by Qt™
Software as part of their Qt™ programming system. This module supports a
number of different database systems through a collection of drivers. Among
the more popular open-source systems for which drivers are available are
MySQL®, SQLite, and PostgreSQL. The module also
supports the 'heavier', more industrial, systems such as Oracle® and IBM DB2®.

With the exception of SQLite, these systems use a client/server model, where
the 'client' software sits on 'your' machine, while the server lives on the
same machine as the database itself, which may be elsewhere on a network. Of
course, in the normal scenario for a personal finance application such as
KMyMoney, 'your' machine acts as both client and server. Your first task
therefore, having decided which database system you wish to use, is to install
the client, and most probably server, software.

In addition to the database software itself, you must also install the
corresponding Qt™ driver module. Most distributions will include driver
modules for the more popular databases. Otherwise, check with the Qt™ software web site and search for
'SQL drivers'

Note

SQLite does not operate on a client/server model; each database is held in a
regular file, local or remote, accessed using the normal methods supplied by
the underlying operating system. In this case, therefore, there is only one
software package to install. Also, some of the following information,
particularly that related to administration, may not apply to SQLite.

Due to limitations in prior releases, only version 3 of SQLite is
supported. Unfortunately, the release of the Qt™ toolkit used by KMyMoney
does not provide a driver for this version. However, an unofficial,
extensively tested, driver is available; if you wish to use SQLite, ask on
(kmymoney2-developer lists.sourceforge.net) for further information.

Administration

Looking after databases is a little more complex than dealing with regular
files. Each system has different methods for performing those necessary
administrative tasks such as creating databases, assigning permissions to
various users, producing backups, etc.. Describing these tasks is outside the
scope of this manual, but all of the supported products provide comprehensive
reference documentation, and a quick search of the web will point you at many
tutorials on the subject.

Creating the database

Code has been included to create an initial database to hold your data if one
doesn't exist. However, it is strongly recommended that you pre-create a
database, because most of the products provide a number of options which may
be relevant. One that may be of particular importance to some would be the
designation of the character set (e.g., UTF-8) to be used for text
fields.

At this time, you will also need to specify permissions for various users to
perform different operations on the database. In most systems, the user who
creates the database will be automatically assigned all permissions, but this
is an area in which the documentation should be consulted.

For your first use of the database, and occasionally at other times when the
database layout changes, you will need permission (also called privileges) to
create and alter tables and views (see next paragraph). There may be different
names for the permission/privilege in different systems, but something like
CREATE and ALTER should be commonplace. For normal running, you will need to
be able to read and write records; these are normally defined in SQL as
SELECT, INSERT, UPDATE, and DELETE permissions.

Creating Tables

On your first use, KMyMoney will attempt to create the necessary table
structures. In order to achieve the maximum compatibility between various
database types, only a subset of common data types are used. There may
nevertheless be situations where a particular type is not supported, and in
this case, provision has been made to generate the SQL code necessary to
create tables. This code can then be modified as required and used to create
the tables outside of KMyMoney. Should you find yourself in this situation,
help can usually be obtained from (kmymoney2-developer lists.sourceforge.net).

Initialisation

Using KMyMoney, open or import an existing data file, or create a new
one. Then select Save as Database from the
File menu. This will present the following dialog:

Database Type

This box lists all Qt™ SQL drivers installed on your system. Select the
driver for your database type. If the one you want is not in the list, you
need to install the appropriate driver. See your distribution documentation,
or visit the Qt™ software web
site and search for 'SQL drivers'.

Database name

The default database name is KMyMoney, but you may choose some other name if
you like. SQLite has one database per file; selecting this driver will open
the standard 'Open File' dialog from which a file may be selected or
created. For some database types, KMyMoney may not be able to create the
database, so it must be pre-created using the appropriate administrative
procedure. However, KMyMoney will create all table structures where
necessary.

Host name

For the average user, the default name of “localhost”, being the
machine you are currently using, is correct. For networked databases, enter
the connected host name.

Note

NOTE: For SQLite databases, the Host name, User name, and Password fields
are not relevant. The SQLite file must have the appropriate read/write
permissions set by the underlying file system to enable the appropriate
access for the currently logged-in user.

User name and password

Check the permissions set up on your database, or contact the database
administrator, for the correct values to use here. The user name must be
capable of selecting, inserting, updating, and deleting records. If the user
name is the same as your login name, a password is not normally required.

Generate SQL

This button will generate the CREATE TABLE commands and save them to a text
file, which may be edited if the in-built commands do not work for your
database system (see previous paragraph).

Accessing your data

Table design

To access your data in KMyMoney, use the Open
Database entry in the File menu. This will
open a dialog similar to the above.

To access your data in other formats, you will need to know a little about how
it is held in relational databases. By far the easiest way to get a feel for
this is to open the database in a front-end such as OpenOffice.org. This
provides a list of the various tables which make up the database, and
enables you to see the layout of each of them.

To extract data, e.g., into a spreadsheet or external file, it is almost
invariably necessary to select linked data from more than one table. This is
done by 'joining' the tables, using a field which is common to each. You can
find a lot more information about how this is done from the online database
tutorials mentioned above. The following table lists the fields used to define
these inter-table relationships.

Field formats

Several of the data fields are held in an internal format which may not be
immediately useful to external programs. In these cases, the information has
been duplicated in both internal and external formats.

Monetary amounts and share values are shown both in numerator/denominator
format, and, with a field name suffixed with 'Formatted', in the form as shown
on your screens.

Similarly, some fields, such as account type appear both as a numeric code,
and in a field suffixed 'String' in the form and language of the application.

Updating your data

Having data in an industry standard format does give you the ability to modify
it outside the KMyMoney application. DO NOT DO IT unless you really know
what you are doing, and always be certain to make a backup copy of your data
first. If you get it wrong, KMyMoney may not be able to access your data,
and you could even end up losing it altogether. You have been warned!

Stored queries

Most database systems allow you to store commonly used queries and procedures,
and in some cases, these may be held as tables or other objects within your
database itself. As you will have guessed from the above, all the tables used
by KMyMoney begin with the lowercase letters 'kmm'. This standard will be
maintained, and only tables beginning with these letters will be
updated. Thus, provided you avoid these in the naming of your queries etc.,
you should not experience any problems.